Additive manufacturing is often seen as a novel alternative compared to well-consolidated, subtractive, and formative manufacturing processes. Its presence in the industrial environment is rapidly ...increasing, and its performance and flexibility may be the answer for present-day fabrication challenges, combining solutions to minimize environmental impacts without losing competitiveness or product quality. Arc welding-based additive manufacturing (also known as wire arc additive manufacturing, WAAM) has been gaining prominence in the current Industry 4.0 scenario. For the advancement of this technology, multiple output analysis of the pertinent welding processes is essential, especially regarding studies applied to materials such as high-strength and high-cost steels. In this paper, a study was conducted with the AISI 420 alloy and CMT variants of the GMAW process applied to additive manufacturing of thin walls, comparing them with conventional GMAW process. The welding processes and deposited welds used were analyzed on electrical, thermal, morphological, and metallurgical aspects. In the end, CMT Advanced and CMT Pulse variants stood out as opposite extremes, whereby CMT Advanced presented the best performance in relation to wall height and heat input. CMT and conventional GMAW produced good and significantly similar results, highlighting the stability of CMT.
TIG welding process with dynamic feeding: a characterization approach e Silva, Régis Henrique Gonçalves; dos Santos Paes, Luiz Eduardo; Okuyama, Marcelo Pompermaier ...
International journal of advanced manufacturing technology,
06/2018, Letnik:
96, Številka:
9-12
Journal Article
Recenzirano
Wire forward and backward oscillation in automatic feeding tungsten inert gas (TIG) process have been pointed as a simple technique to achieve high productivity levels and process stability for a ...wider operation range, compared to the conventional version. However, in this case, physical aspects related to the involved phenomena are still not fully understood. Based on that, the present paper addresses a characterization analysis of low frequency dynamic wire feeding process, in order to yield some contribution to the knowledge gain of these phenomena. Both conventional automatic feeding and autogenous process were taken as a reference. The study covers system description as well as metal transfer modes, welding pool temperature gradient, and respective weld geometry. Bead on plate welding was performed and monitored with high-speed and thermographic cameras. Dynamic oscillation showed good stability and proved to be more flexible among other versions, as feeding speed and power do not need to be correlated. In order to enable proper wire dynamic movement monitoring, a special motion measuring system was developed.
Over the last years, a profusion of new versions of arc welding processes has overwhelmed the international welding scenario in the industry and academia. Innovations have been made possible not only ...by means of electronics and software developments but also through new concepts in mechanical design and mechanisms. With respect to the tungsten inert gas (TIG) process, low productivity is often a disadvantage, when compared to other arc welding processes. In order to manage this drawback, as well as to better deal with hard wetting materials (Ni-Cr alloys for example), a forward and backward wire oscillation movement has been implemented in TIG systems and finds good acceptability in the industry. However, dedicated wire feed measuring systems for this new operating regime are not available, which limits the process monitoring as a whole and hinders phenomena understanding and parametrization stage. The present paper thus addresses the development of a measuring methodology combined with a transducer, based on an optical encoder, for acquisition of instantaneous angular speed (IAS). The study covers analysis of the performance of previous instrumentation (found unsuitable), description of the dedicated system, and verification methodologies. Results lead to the validation of the system. Therefore, valuable information can now be extracted to provide feedback for this welding process version and avoid instabilities.
This work presents new research results from double-electrode gas tungsten arc welding, a process variant that was developed with the aim of improving productivity and welding speed. A welding torch ...specially constructed for research was used with total current in the range of 200–600 A. Tests using a high-speed camera were conducted in order to characterize the arc morphology at different distances between the electrodes. It could be seen that the morphology of the arc and the voltage drop in each electrode change significantly with the increase in the welding speed, especially when there is a larger clearance distance between electrodes. The resulting arc presented bigger asymmetry as the welding speed was increased. Bead-on-plate tests were performed in order to evaluate their susceptibility to humping defects. The results showed that in comparison with the conventional GTAW, the double-electrode process enables a considerable increase in the maximum speed, without defects—taking into consideration the total applied current. This shows that this new process has great potential for expanding the range of gas tungsten arc welding in high-productivity welding applications.
Welding processes are present in most industry sectors. Conventional arc welding processes, such as the gas metal arc welding (GMAW) process, have limitations when applied to join thick materials. In ...this scenario, the laser beam welding (LBW) process has proved to be an alternative to achieve high penetration depths, eliminating the need for joint beveling, although not without limitations. Proneness to surface and internal discontinuities are some of them. Recently, hybrid laser-arc welding (HLAW) process has come up as a promising joining process, combining the advantages of the GMAW and LBW processes on a single melting pool, counteracting defects, and enhancing process efficiency. Despite the high complexity of the hybrid process, its advantages derive not only from geometrical and mechanical issues but also from metallurgical features or characteristics. Twelve LBW and HLAW welding tests were performed using 5, 6, 7, 8, 9, and 10 kW of laser power. The HLAW results show higher robustness against weld defects, as well as greater penetration depths and bead widths then pure LBW. The microstructures in all regions of the welds were analyzed, showing their correlation between the welding parameters and processes performed. Due to a distinct thermal cycle resulting from the two simultaneous heat sources, the weld bead produced by the HLAW process presented reduction of 100 HV in the microhardness on the upper region and consequently reduction of its brittleness. The results obtained clearly indicate the metallurgical and operational advantages of the HLAW process compared with the individual LBW process.
Gas protection is very important in arc welding processes and several factors influence its effectiveness. This paper provides a discussion of the applicability of the Schlieren technique to arc ...welding processes. Tests were performed with different types of shielding gas and with GMAW and GTAW torches, in order to highlight differences associated with the various conditions. The results obtained in conjunction with a review of results reported in the literature allowed an evaluation of the limitations associated with the use of the Schlieren technique in the arc welding processes. The most important limitation is that the visualization is inherently difficult when using pure Ar gas, meaning that in most situations it is not possible to adequately visualize the flow interface with atmospheric air, which is the main region of interest in this type of analysis. However, visualization is possible in regions where pure Ar is heated, or when mixtures with other gases are used. In addition, the results obtained with different sources of light were compared and the test was performed by filming the arc welding or with the gas flowing through the torch without the arc. The differences observed in the results obtained are discussed herein.
This study focused on the improvement of an adaptive orbital welding system, applying a laser-based vision sensor, with the objective of increasing its reliability and robustness by proposing a ...calibration for the manipulator’s rail deformations, and also developing novel methods and algorithms based on neural network techniques for the adaptive parameters setup. The main problem with mobile-based robotic welding systems that use computer vision for trajectory control arises from the offset between the sensing point and the welding torch, in conjunction with the geometric deformations of the mounted rail. This configuration in moving base manipulators generates an error on the online trajectory correction. In this context, methods of verification and calibration of this systematic error intrinsic to the geometric composition are necessary. Welding tests were conducted in order to validate the proposed methods, for both rail form calibration and adaptive welding parameters setup. The enhanced system was capable of overcoming significant geometrical variations of the gap and pipe mismatch. A previous scan was used to calibrate the rail deformation, allowing for single laser line projection sensors to be utilized for this purpose. The proposed methods are restricted to not only welding operations of large-diameter pipes, but also for general welding applications and possible inspection operations as well.
Most of pipeline welding still applies manual procedures, which increase production time and is stressful to the welding operator. This happens mainly due to the accurate melt pool control that hand ...operation enables. It yields high flexibility between material addition and heat source and is therefore adaptable to the welding condition and situation of each moment. This feature is not fully found when mechanized welding with automatic feeding is performed, despite every benefit of welding automation. This renders an optimized parameterization of a complex task. Automatic orbital welding is already a reality, though only applied in large scale in developed countries and/or by few expert companies from developed countries, due to such controllability, repeatability, and robustness difficulties. In this paper, a concept for dynamic wire feeding and respective implementation and analysis are presented. It consists of a low-frequency wire speed oscillation, aiming to decouple wire speed and arc power to a larger extent, which approaches to manual procedure as it guarantees user flexibility, but still keeping the benefits of welding automation. ASTM 139 Grade D tubes were welded under stable processing conditions. The macrographs did not indicate discontinuities such as porosity or lack of fusion, resulting in complete joint penetration. The average welding speed reached was 27.8 cm/min (10.9 in/min), much higher than that found by other authors.
In conventional MIG/MAG welding process, the root of some of the most frequent problems is related to current variation due to solid wire electrode extension (stick out) alteration. This becomes most ...relevant in semi-automatic welding procedures, where the welding operator is responsible for holding the torch. Inevitably, the contact tip-to-workpiece distance, and as a result, the stick out length, will oscillate due to operational difficulties, such as complex geometry and out-of-position welding. Since the average current has decisive influence over various weld properties, variations in its values incur in reduction of process and weld regularity, repeatability, robustness and reliability. The present work investigates and quantifies the effects such as current drop and electrode temperature profile based on well-known theoretical–analytical concepts under an application oriented standpoint, so as to scientifically support research and development of modern MIG/MAG welding adaptive systems. Results pointed a higher wire preheating degree in spite of lower current levels when stick out is increased. Experiments showed a weld bead geometrical reduction, which can be avoided through an intelligent system, capable of identifying welding current behavior, electrode voltage fall and electrical resistance curves for process online correction and prevention of possible defects.
The switch back technique consists of an oscillatory movement of the torch applied in the longitudinal direction of the welding. This method has already been studied with the MIG/MAG process in ...different works which indicated the advantages of its use. The most relevant impacts concern the increased welding speed and the robustness of the procedure, which could potentially be transferred to other welding processes. This paper innovatively presents the study of the switch back technique for the TIG process at high currents. The activities involved the development of robotic infrastructure for the application and development of the respective procedures, as well as special techniques to monitor the welding. The results showed that switch back applied to the TIG process could greatly contribute to a decrease in the incidence of defects, which opens the possibility for developing high-productivity procedures.
